The invention is based upon a process for detecting the stroke motion of a body which is displaceable in a housing.
Processes of this kind are necessary for example in order to be able to reliably detect the precise stroke course of a valve member of an injection valve as a function of its injection pressure during the entire injection time, in particular of an injection valve inserted into the combustion chamber of an internal combustion engine. In modern internal combustion engines, the course of the fuel injection, which is influenced by injection pressure and valve member stroke, is of great significance since the combustion process in the combustion chamber can be considerably influenced by these factors, in particular with regard to pollutant emissions and fuel consumption.
Thus the combustion pressure peaks produced by ignition delay in auto-ignition internal combustion engines can be prevented by subdividing the fuel injection into a pre-injection quantity and a main injection quantity. For this kind of subdivision of the course of injection, the opening stroke motion of the valve member of the injection valve is divided into two phases; in a pre-injection phase, first only a small injection volume is released by the mobile valve member, and in an ensuing injection phase the entire injection volume is released. For this kind of embodiment of the opening stroke motion of the valve member of the injection valve, as disclosed for example in German Utility Model 92 059 759, two valve springs which act on the valve member in the closing direction are provided on the injection valve, of which a first valve spring constantly acts upon the valve member and a second valve spring engages the valve member only after it executes a pre-stroke in the opening direction. The injection pressure acting on the valve member in the opening direction first brings about an opening stroke motion (pre-stroke) of the valve member counter to the restoring force of the first valve spring, by means of which the injection cross section which determines the pre-injection quantity is opened. After the pre-stroke is carried out, the valve member comes into contact with the second valve spring; the pressure increase of the fuel delivered to the injection valve now is no longer sufficient to overcome the force of both valve springs, so that the valve member pauses for a short time in its stroke position. With the further pressure increase of the fuel, then the force of the second valve spring is also overcome, and this opening stroke motion of the valve member counter to the force of both valve springs now opens the entire opening cross section at the injection valve, so that the main injection quantity reaches the combustion chamber of the internal combustion engine via the injection opening.
To optimally adapt the injection valve to the requirements of the respective internal combustion engine, it is necessary to be able to precisely adjust the time of the pre-injection and consequently the pre-injection quantity, or to precisely adjust the onset of the main injection, which depends directly on injection pressure at the injection valve.
To determine the time of the onset of the main injection as a function of the pressure increase in the injection line leading to the injection valve, German Patent Application 41 08 416, U.S. Pat. No. 5,271,270, for example, discloses the insertion of a so-called needle motion sensor into the injection valve; this sensor detects the course of the stroke motion of the valve member electromagnetically or in a directly mechanical manner and registers it via a display device. At the same time, the pressure in the injection line is determined via a pressure sensor whose measurement values are likewise plotted over time so that an injection pressure value can be assigned to the onset of the second stroke phase (main injection), which appears as a plateau which adjoins the pre-injection stroke in the course of the opening stroke. In this manner, when there is a predetermined injection pressure value, the time of the onset of the main injection can be adapted to the respective requirements via changing the prestressing of the valve springs and adjusting the pre-stroke path of the valve member (the same is true for the closing of the valve).
The known measurement process, however, has the disadvantage that the needle motion sensor must be inserted into the injection valve and, since it is an expensive component, cannot remain there, but must also be removed again, which results in a high assembly expenditure and makes this measurement process particularly unsuitable for controlling mass production.
Another known process, in which the time of the onset of the second opening stroke of the valve member is determined only from the course of the pressure in the injection line (change in the speed of pressure increase), is not precise enough because of the very short times and dynamic effects, particularly with injection valves which operate at high pressures.